He fantasized, vividly, about sex with Ashanti. He sent close-up shots of his hand on his own genitals. The language was filthy, the barrage of voice, text and photo messages virtually non-stop.

“I’m thinking, in my mind, rape,” the R&B superstar’s mother and manager told a jury yesterday, day one of the stalking trial of Ashanti-obsessed fan Devon Hurd.

“My job is to be her manager,” added Tina Douglas — to whose phone the Indiana resident sent his vile fusillade.

“But she’s my daughter, first.”

Douglas and her husband — Ashanti’s tour manager — have raised Ashanti and a younger daughter in the same Glen Cove, Long Island, home the couple has shared for 30 years.

Yesterday, Douglas took the witness stand in Manhattan Supreme Court described how that happy household — buzzing with the successful business of a beloved international recording star — was rocked by the intrusion of Hurd’s depravity.

The mom still doesn’t know how Hurd got her business number, except that managing Ashanti means dealing with “thousands” of people in the recording, television, film and theater worlds — too many contacts to simply change the number, she told jurors.

Hurd’s contacts began in 2006, with phone calls, she testified. The first year of messages were merely annoying.

“He’d be going on about her music and Ashanti, and who she is and what’ she’s doing,” the mom told jurors. “It was just rhetoric and garbage.”

She tried ignoring him. She tried telling him stop it — even cursing him out on the phone. But by this year, Hurd’s messages had turned ugly. This past summer, when Ashanti starred as Dorothy in a revival of The Wiz at City Center, Hurd sent dirty texts indicating he knew the location of her work, her home, and her plans for the night. He even sent a photo of her car, parked outside the theater.

“We’re all adults here,” said Douglas — a beautiful woman in a stylish brown wool dress suit who looks more like Ashanti’s older sister than her self-described “momager.”

Then, with hardly a flinch, she described for jurors the content of Hurd’s worst correspondences.

“He wrote that ‘I want to f— her; I want to do this to her; I want to marry her; I might f– you,” the mom said.

When assistant district attorney showed jurors, on an overhead screen, a photo Hurd took of himself while masturbating, Douglas again, unflinchingly, narrated.

“To look at it now — and I’ve been looking at this — the shock value just never goes away,” she told jurors, her voice firm. “It’s very, very frightening.”

“I sickened by it,” the mom said.

Hurd, 31 — whose profession is unclear — argues he is merely a fan who has a bad way with words — though even the lawyer, Richard Verchick, concedes Hurd’s messages were “despicable,” and “gruesome=” just not illegal.

“Now it’s misguided, and it may be sick, but it’s not criminal,” the lawyer told jurors in opening statements.